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D2.Community - Community Ecology Biodiversity Levels of...

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Community Ecology Heyer 10 Community Ecology Community Ecology part 2: part 2: Biodiversity Biodiversity Biodiversity Levels of biological diversity Biodiversity Species richness = # species/area Relative abundance = proportion of total diversity taken up by a few dominant species species richness + relative abundances biodiversity stability N.Am. bird species diversity Two communities can have the same species richness, but a different relative abundance • A community with an even species abundance is more diverse than one in which one or two species are abundant and the remainder rare Figure 54.9 Community 1 A: 25% B: 25% C: 25% D: 25% Community 2 A: 80% B: 5% C: 5% D: 10% D C B A Estimating Community Diversity Shannon Diversity Index (H) Estimating Community Diversity Shannon Diversity Index Community 1 A: 25% B: 25% C: 25% D: 25% Community 2 A: 80% B: 5% C: 5% D: 10% D C B A A: (0.25 x ln 0.25) B: (0.25 x ln 0.25) C: (0.25 x ln 0.25) D: (0.25 x ln 0.25) ------------------------ = 1.39 = H A: (0.80 x ln 0.80) B: (0.05 x ln 0.05) C: (0.05 x ln 0.05) D: (0.10 x ln 0.10) ------------------------ = 0.71 = H
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Community Ecology Heyer 11 Dominant Dominant Species Vegetation with the highest density and/or biomass redwoods In addition to habitat complexity, other major factors related to community diversity: • Climate – especially water availability (b) Vertebrates 500 1,000 1,500 2,000 Potential evapotranspiration (mm/yr) 10 50 100 200 Vertebrate species richness (log scale) 1 100 300 500 700 900 1,100 180 160 140 120 100 80 60 40 20 0 Tree species richness (a) Trees Actual evapotranspiration (mm/yr) Figure 53.25 In addition to habitat complexity, other major factors related to community diversity: Available geographical area for the community Area (acres) 1 10 100 10 3 10 4 10 5 10 6 10 7 10 8 10 9 10 10 Number of species (log scale) 1 10 100 1,000 Figure 53.26 Biodiversity Hot Spots A biodiversity hot spot is a relatively small area with an exceptional concentration of endemic species and a large number of endangered and threatened species Particularly resulting from habitat destruction. Most impacted biomes: – Tropical rain forest – Chaparral Terrestrial biodiversity hot spots Equator Figure 55.17 Extinction is forever Extinction is forever Endangered species In immediate danger of becoming extinct throughout its range Hundred-heartbeat Club <100 individuals left! Threatened species Likely to become endangered in the foreseeable future if current trends continue (a) Philippine eagle (b) Chinese river dolphin (c) Javan rhinoceros Hundred-heartbeat club-members The Extinction Vortex Small population Inbreeding Genetic drift Lower reproduction Higher mortality Loss of genetic variability Reduction in individual fitness and population adaptability Smaller population A diminished population is prone to positive-feedback loops that draw the population down an extinction vortex Once population size is reduced to a critical level [the Minimum Viable Population ], it may not be able to recover!
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Community Ecology Heyer 12 “On a global basis...the two great destroyers of biodiversity are: 1. habitat destruction , and 2. invasion by exotic species The Nature Conservancy /
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